I. Field of the Invention
This invention relates generally to implantable cardiac rhythm management devices, and more particularly to a method of operating such devices to more correctly classify ventricular beats occurring after an atrial depolarization (either paced or sensed) as an ectopic beat, i.e., a beat of non-sinus origin.
II. Discussion of the Prior Art
A drawback of many present-day automatic implantable defibrillators and cardiac pacemakers is that they normally only identify as a premature ventricular contraction (PVC) a beat that is not preceded by a sensed atrial depolarization. Yet, it has been shown that frequently such ectopic beats do occur following an atrial event. When the implantable device fails to detect ectopic beats, inappropriate indicators can be recorded on the device's stored electrogram. When the electrogram is then read out by a physician, the improperly marked recording strip can lead to errors in diagnosis and/or treatment.
Ectopic ventricular beats that occur after an atrial sense/pace event may be examples of late coupled PVCs, which some authors have discussed as common onset patterns for arrhythmias. Thus, the ability to better detect late-coupled PVCs is important for beat trending and arrhythmia prediction purposes.
The inability to detect all PVCs may also lead to life threatening pacemaker mediated tachycardia (PMT). It is found that in some patients multiple episodes of PMT due to retrograde conduction of an ectopic ventricular beat resulting in the pacer tracking at its maximum tracking rate. To address PMT, state-of-the-art pacemakers and pacemaker/defibrillators employ what is called “post ventricular atrial refractory periods” (PVARP) following a PVC to prevent PVCs from starting a PMT episode. The length of the PVARP tends to be fixed. However, ectopic beats may occur after an atrial sense event, such that the implantable cardiac rhythm management device classifies such beats as a normal ventricular sensed event instead of a PVC. Since there is only a short atrial blanking after a ventricular sense event, these ventricular ectopic beats may have retrograde conduction, causing an erroneous premature atrial sensed event that leads to a PMT episode. The use of a fixed size PVARP after a PVC with post atrial sense PVCs results in undersensing at high rates. By providing a dynamic-sized (rather than fixed) PVARP following an ectopic beat, it can blank the atrial channels after the ectopic beat, retrograde conducted ectopic sensed beats will be prevented from causing PMT, yet at the same time will allow sufficient atrial blanking without atrial undersensing.
In addition, proper identification of non-sinus ventricular beats is critical for heart-rate variability (HRV) measurements, since HRV measurements require intervals that are sinus in origin. HRV, or actually the lack thereof, is a factor in assessing the severability of congestive heart failure. For a discussion of HRV as an indicator of CHF, see “Depressed Heart Rate Variability as an Independent Predicator of Death in Congestive Heart Failure Secondary to Ischemic or Idiopathic Dilated Cardiomyopathy” by Piotr Ponikowski, et al., The American Journal of Cardiology, Vol. 79, Jun. 15, 1997, pp. 1645–1650. Thus, a need exists for a method that can more reliably discriminate between sinus and non-sinus ectopic ventricular sensed beats.